This invention relates to a multi-layer film having a metallized surface having superior metal adhesion and excellent fracture resistance.
The bonding of metals such as aluminum, silver, chromium, etc. to plastic films has allowed such films to replace such metallic foils in many instances. The flexibility of the films necessitate the formation of a strong metal-plastic bond, and a number of approaches have been developed for providing such bonding.
In U.S. Pat. No. 4,345,005, the disclosure of which is incorporated herein by reference in its entirety, a homopolymer polypropylene core layer is co-extruded with an ethylene propylene copolymer. The film is biaxially oriented and the copolymer layer is corona treated. A metal coating is deposited on the corona treated layer by a suitable process such as vacuum deposition. In order to enhance adhesion between the metal and the plastic film neither the core layer, nor the outer layers contain a slip agent in an amount which would deleteriously affect the bond between the metal and plastic film.
Other approaches to providing a good metallizable surface have included modifying the surface of a polyolefin film with various oxidation processes and/or applying an adhesive to the surface of the film. Various primer coatings have been employed for this purpose, including carboxylated butadiene polymers and maleic anhydride modified static propylene polymers.
It is an object of the present invention to provide a multi-layer polymeric film having a metallized layer strongly bonded thereto. It is another object of the present invention to provide a metallized film having excellent metal fracture resistance. Yet another object of the invention is to provide a metallized film having low water vapor and oxygen transmission rates.